The invention relates to data acquisition systems in which a plurality of remote analog inputs are monitored and controlled from a central location and in digital form by a computer.
It is known from U.S. Pat. No. 3,530,458 of F. G. Willard et al. to use a centrally located oscillator and counter for deriving a count in relation to multiplexed analog inputs for the purpose of point measurement, noise reduction, digital gain and zero calibration under control of a computer.
It is known from U.S. Pat. No. 4,068,306 of A. C. Chen et al. to control with a computer the application of local reference signals for calibration purpose and of an analog input to a local integrator for deriving a count to be utilized by the computer with other counts derived by multiplexing from a plurality of possible single point measurement locations.
It is also known from U.S. Pat. No. 3,916,173 of R. B. Williams et al. to make scale and zero corrections with a computer in relation to a plurality of analog input signal measurement channels for passive zeroing.
The three above-identified patent references indicate that digital treatment with a computer is advantageous for monitoring and control of a plurality of single point analog input measurement channels, in particular for offset correction and calibration as well as measurement. Nevertheless, the prior art has not been able to use this central computer approach to the maximum advantage.